1. Field of the Invention
The present invention relates to the control of a voltage regulator having a plurality of switching field-effect transistors (FETs).
2. Background of the Related Art
Modern central processing units (CPUs) experience extreme current transients, some on the order of 100% above the maximum steady state current. Depending on the design of a voltage regulator providing power to the CPU, load changes can be in the hundreds of amps, at very high slew rates. In order to meet these high current requirements, the voltage regulator usually requires an inductor having very high current saturation limits. However, such an inductor may become rather large since the physical size of an inductor is proportional to its current saturation limits.
Furthermore, age, temperature, and manufacturing imperfections can cause the current saturation limits of the inductor to become compromised or unable to perform to the inductor's specification standards. A primary concern is that an inductor with compromised performance can lead to current runaway on the power stages of the voltage regulator that provide current to a load such as the CPU.
FIG. 1 is a schematic diagram illustrating a drop in inductance of an inductor due to current saturation and the resulting current ripples that can damage various components, such as field-effect transistors of the voltage regulator. As the current flowing through the power stages and the output inductor increases near the point of current saturation, the effective inductance of the inductor core begins to decrease, thus increasing the peak current of the associated phase. As the effective output inductance decreases, the ripple current through the output inductor increases, causing undue stress on the power stage of the voltage regulator. If left unchecked, this increased ripple current can damage the switching field-effect transistors of the voltage regulator.